1. Field of the Invention
The present invention is generally in the field of semiconductor devices. More specifically, the invention is in the field of output drivers for semiconductor devices.
2. Related Art
Integrated circuit (IC) devices, such as application-specific ICs (ASICs), are typically utilized on system boards for communication devices, such as cellular handsets, as well as other types of electronic devices. These IC devices employ output driver circuits that have output drivers with fast edge rates to generate square wave logic outputs. However, the sharp edges of the square waves generate harmonics that create undesirable radio frequency (RF) noise. The RF noise caused by harmonics generated by the sharp edges of the square waves can interfere with the RF-sensitive components, such as the RF receiver front end of a communication device.
One conventional approach to solving the RF noise problem discussed above includes isolating the output driver circuit from RF-sensitive components. Isolation between the output driver circuit and RF-sensitive components can be achieved by increasing the separation distance between the output drivers and the RF-sensitive components or by enclosing the output driver circuit in a shielded environment. However, both of the above isolation methods undesirably increase the cost of the final product.
Another conventional approach includes reducing the speed of the output drivers in the output driver circuit by utilizing filtering or by reducing the size of the output drivers. However, filtering requires additional system board space and results in increased power consumption, while reducing the size of the output drivers leaves the output drivers more susceptible to load capacitance, which can prevent the output driver circuit from maintaining the required output data rate. Additionally, reducing the size of the output drivers increases the crossover time in which both upper and lower output drive transistors are simultaneously on, which causes an undesirable increase in power consumption by increased “crowbar current.”
Thus, there is a need in the art for an output driver circuit in an IC device, such as an ASIC, that generates reduced RF noise, consumes less power, and has reduced susceptibility to output load capacitance.